Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

690
FXUS63 KLOT 022330
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
630 PM CDT Thu Jul 2 2026

.KEY MESSAGES...

- Heat and humidity will continue on Friday, though the worst
  conditions (heat indices up to/around 105F) will likely focus
  near/south of the Kankakee River. On Independence Day, peak
  heat indices of ~95-100F are expected near and south of I-80.

- Waves of thunderstorms are expected through the weekend,
  though there will be many dry hours. Any thunderstorms on
  Friday will be capable of producing damaging winds. There will
  also be a threat for at least localized flash flooding with
  any focused corridors of thunderstorms through the weekend.

&&

.DISCUSSION...
Issued at 315 PM CDT Thu Jul 2 2026

Through Early This Evening:

The outflow boundary that served as an impetus for isolated
convection (showers and a few thunderstorms) near and north of
I-80 has mostly washed out, taking away the enhanced lower level
convergence. As such, given capping, and mid-level dry air and
subsidence in place for most of the area, the threat for
additional convection will be minimal through sunset. A minor
exception will be into portions of central Illinois, as widely
scattered showers and storms developed near and south of a PIA
to DNV line. RAP analysis and near term forecasts indicate a
pretty sharp mid-level moisture gradient into our central IL
counties, so any thunderstorms that do manage to reach into far
southern areas may tend to dissipate with farther northeastward
extent.

Tonight-Early Friday:

Strong to severe thunderstorms ongoing as of this writing across
the Upper MS Valley are tied to a low amplitude short-wave
emanating from the Central Plains, interacting with a much less
capped, more strongly unstable environment in that area. While
the strongest large scale forcing will generally remain north of
our area tonight, expectation is for a combination of erosion
of capping and possibly congealing outflows from storms just to
our to north and northwest to yield increasing thunderstorm
coverage with time.

The exact extent of convective coverage is still a bit unclear,
so opted for scattered wording in the grids near/north of I-80.
The threat for storms should start earliest near the IL/WI
state line (mainly after 8 or 9pm) and then build south later in
the evening and early overnight. With a large instability
reservoir, high PWATs (conducive to precip loading and wet
microbursts), DCAPE still upwards of 1k J/kg, and modest deep
layer shear, the main thunderstorm threat will be damaging wind
gusts. It`s certainly plausible that some of our far northern IL
counties will need to be included in a convective watch this
evening.

If more organized clusters/lines of storms are able to develop
and send a coherent outflow boundary farther south prior to
exhaust of available MUCAPE, we`ll also need to watch for
corridors of training convection and an associated flash
flooding threat, most favored across far northern Illinois.

Shower and thunderstorm coverage is then expected to wane after
4 AM or so and translate to a primarily dry start to Friday.
However, we did hold onto slight chance PoPs from 7-10 AM to
account for rogue lingering convection.

Heat and Humidity on Friday:

Similar to today, lingering outflow boundaries, any associated
wind shifts, and outflow modified profiles are quite plausible.
Sufficiently high thunderstorm coverage tonight and sagging
outflows tonight could somewhat delay air mass recovery with
northward extent (and vice versa). All in all, the lower
thunderstorm coverage expected tonight south of I-80 should
enable an earlier jump on diurnal warming, plus higher dew
points (solidly mid to locally upper 70s) are forecast.
Therefore, confidence is highest in peak heat indices
approaching or locally exceeding 105F for locations near and
south of the Kankakee River. With Friday being day 5 of the
current heat wave, felt the path of least regret was to extend
the Extreme Heat Warning until 7 PM CDT Friday for the
aforementioned locales. Depending on convective evolution this
evening into early Friday, we may need to consider changes to
heat headlines (the warning for the rest of the area expires at
midnight CDT tonight).

Castro

Friday Afternoon-Evening Convection:

A more potent wave currently crossing northern Arizona will
become another focus for convection over our area on Friday.
This wave will cross northern IL and southern Wisconsin during
the afternoon, setting the stage for a potential line or
clusters of thunderstorms in the area Friday afternoon into the
early evening traversing northern Illinois into northwest
Indiana. Inevitably, effects of prior convection (or lack
thereof in spots) can be expected to augment the location and
timing of convective initiation, lowering confidence in
specifics. With this afternoon`s forecast issuance, we`re
messaging a favored timing of about 1 PM to 7 PM CDT for highest
thunderstorm coverage on Friday (earliest west, latest east). Modest
deep layer shear and an inherent high DCAPE reservoir with the
warm/humid airmass support the risk for damaging winds with any
linear segment or multicell clusters.

Conceptually, subsidence in the wake of the short-wave and
associated convection should result in a steady downward trend
in thunderstorm coverage the remainder of Friday evening, which
*may* bode well for late evening community fireworks displays.
It`s certainly too early for an all clear area-wide in that
period (mid-late Friday evening), though there has been a
somewhat consistent signal (including in products such as the
HREF calibrated thunder probabilities) in lower convective
coverage to be able to note this in our graphical messaging.

Castro/Kluber


Friday Night Onward:

A mid-level impulse exiting the northern Rockies late on Friday
will provide renewed convective episodes in the region as the
mid-level pattern becomes zonal. The track of this convection
will likely focus along an effective cold front produced by the
combined effects of convection over the next 48 hours. So while
convection seems likely in the region on Saturday/Independence
Day, the location of convection could range from southern
Wisconsin to southern Illinois. Furthermore, with forecast
guidance consistently depicting a slowing or stalling mid-level
wave over the western Great Lakes late Saturday into early next
week, timing out precip chances becomes even more difficult if
not impossible.

As the aforementioned wave eventually drifts eastward, drier
and somewhat cooler conditions are expected by the middle of
next week.

Kluber

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 630 PM CDT Thu Jul 2 2026

Key Aviation Messages for the current TAF period:

- Scattered showers and thunderstorms this evening and possibly
  into the overnight.

- Additional thunderstorms during the day on Friday, most likely
  during the afternoon.

Southwest wind gusts around 20 knots and VFR conditions prevail
in the immediate short term. However, outflow from storms in
southwest Wisconsin is surging southward into northern Illinois.
Winds with the outflow could turn to the northwest, with
scattered showers and storms moving in behind it. Increased
confidence in arriving around KRFD prompted not just an earlier
time of arrival, but converting the PROB30 to a TEMPO.

Models are suggesting that this outflow will continue to move
southeastward with a broken line of showers and storms moving
along with it. But as the outflows moves away from the storms,
they should be arriving in a decaying state. This adds some
uncertainty in timing and location of storms specifically,
keeping the chances as a PROB30, for now, though the arrival
time was bumped up based on current observations. There is lower
confidence in showers/storms remaining behind this round. As a
low level jet increases in the pre-dawn hours, there is a
chance that elevated convection could tap into a region of
instability resulting in the need for VCSH/VCTS through 12Z.
For now, it was decided to see what occurs with the first round
and then potentially adding additional precipitation mention at
the 06Z TAFs.

Winds will return to the west southwest tomorrow. Other than
some lingering showers in the morning, a drier period in the
morning is expected for most terminals. The next impulse is
expected to move over northern Illinois from the west in the
late morning to early afternoon prompting PROB30 mentions for
TSRA at all the TAF sites.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Extreme Heat Warning until midnight CDT tonight for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ019-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-
     ILZ108.

     Extreme Heat Warning until 7 PM CDT Friday for ILZ023-ILZ032-
     ILZ033-ILZ039.

IN...Extreme Heat Warning until midnight CDT tonight for INZ001-
     INZ002.

     Extreme Heat Warning until 7 PM CDT /8 PM EDT/ Friday for
     INZ010-INZ011-INZ019.

LM...None.

&&

$$

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